1. Field of the Invention
The present invention relates to a power converting device for an electric train.
2. Description of the Related Art
In a power converting device for an electric train, for example, Japanese Examined Utility Model Application Publication No. H3-21901 discloses a conventional technology concerning a power-running notch command, in which an opening timing of the power converting device is shifted for each unit when an OFF signal of the power-running notch command is input (i.e., the power-running notch command in ON state enters OFF state), to prevent an abrupt rise of an overhead line voltage when an overcurrent is flown into the power converting device.
Japanese Patent Application Laid-open No. S61-58405 discloses a technology for driving an electric train by changing the voltage-to-frequency ratio of output of a power converting device and a slip frequency of an AC motor such that the electric train is operable in a substantially no-load condition after input of an OFF signal of a power-running notch command other than a minimum notch command, or an input of an OFF signal for braking in an regenerating area. In this manner, an optimum coasting characteristics of the electric train can be obtained.
When an OFF signal of the power-running notch command is input, a torque is sometimes generated in the AC motor, which may accelerates the electric train. In a railyard or an inspection yard where the electric train is inspected, a notch command is repeatedly turned on and off to stop the electric train slowly at a specified position. If the electric train is accelerated with the torque generated when the OFF signal of the power-running notch command is input, the electric train can hardly be stopped at the specified position.
In a typical electric train, a power-running notch command is issued via a drive lever provided in a driver's cab. Based on the power-running notch command, a power-running torque command is decided. When the power-running notch command is turned OFF, the power-running torque command gradually becomes zero as shown in FIG. 3. When such control is performed, although a shock can be reduced, the electric train may be accelerated depending on the situation, which makes it difficult to stop the electric train at a specified position. Especially in a railyard and an inspection yard, the electric train is required to stop at the specified position with a strict tolerance, and thus, there is an increasing demand for a technology for stopping the electric train at a specified position precisely.